The present invention concerns the improved process for preparing 2-(2,4,6-trichlorophenoxy)-ethyl chloride and N-n-propyl-N-2-(2,4,6-trichlorophenoxy)ethyl amine and their use in the manufacture of Prochloraz.
2-(2,4,6-Trichlorophenoxy)-ethyl chloride and N-n-propyl-N-2-(2,4,6-trichlorophenoxy)-ethyl amine are used as intermediates in preparing the fungicide Prochloraz.
According to GB 1,469,772, the classical method of preparing Prochloraz begins with 2,4,6-trichlorophenol. This process suffers from several disadvantages. First of all, the trichlorophenol must be in a highly pure form to avoid the formation of tarry by-products in the subsequent steps of preparing Prochloraz. Second, the processes used to purify 2,4,6-trichlorophenol most often lead to the formation of undesireable chlorinated by-products. Furthermore, the use of 2,4,6-trichlorophenol to prepare Prochloraz requires the reaction of the former under basic conditions, which can also lead to the formation of similar chlorinated by-products.
Recent reports have tried to avoid the problems. Thus, EP 243,038 describes a process of preparing 2,4,6-trichlorophenol involving the slowcontrolled chlorination of phenol in the presence of a catalyst which is alleged to diminish the formation of the chlorinated by-products. EP 299,892 describes the chlorination of a chlorophenol using a different type of catalyst.
Nevertheless, even if the formation of unwanted chlorinated by-products are avoided, the standard process for preparing Prochloraz according to GB 1,469,772 involves the need to handle 2,4,6-trichlorophenol and ethylene dibromide--themselves both highly toxic and carcinogenic materials.